To date, I’ve been storing my original shipping boxes for my audio equipment… the garage is really quite stuffed w empty boxes in hope that some day, should I decide to sell my equipment, I would ship w the original boxes…
At what point do you just say…" I no longer have the room" or " i will never get rid of some of my equipment " and just get rid of those space gobbling containers…about a year ago I needed to ship an old heavy amp ( I did not have the original shipping container ) that I sold and needed to be shipped…by the time I went to HDepot for multiple boxes, got styrofoam ,manual cutting and fitting to double box the amp, I spent over 4 hours and several rolls of heavy duty shipping tape to ensure a safe shipment. I am anticipating the purchase of new “larger” speakers and am contemplating what to do w those additional 5ft boxes…
I saved all my boxes in the garage too. Luckily my speaker boxes are big enough to contain all the equipment boxes within. So I guess bigger speakers have fringe benefit 
People, including me, put a high value on original boxes. But rather than dedicate enormous space to empty boxes, I have discarded several and then purchased new boxes from the manufacturer at sale time. I’ve done this with PS Audio and Pass Labs with no issues.
besides, the empty boxes can get moldy in my garage…
I bought super humongous plastic bags off Amazon and put my boxes in those. Taped them shut with duct tape and then put the boxes in the attic (only place I had room). Figured bagging the boxes would keep moisture and bugs away.
I keep everything always forever, but I don’t have half as much gear as many others do.
In one case the resale value was higher because I had the original boxes and documents.
Edit to add that most are stored in the garage, typically inside larger boxes, without any problems.
Like others, I put a premium on original boxes, whether I’m buying or selling. Also, like @algaudio mentioned, coming up with suitable replacement boxes and packing materials can be a grind.
Fortunately, I have adequate attic space to store them. It’s really nice that when I go to sell a piece of gear, I have everything I need.
The original box and documents also convey, “This is not a knockoff product”.
That’s a good idea. I found Amazon sells bathtub liners that are big enough to cover the boxes for FR30 speakers. I’ll order some to try.
Not saving the original boxes becomes a problem and a headache as you discovered and for reasons others have mentioned. I rented a storage unit to get rid of some other clutter from my basement as I prepped my new man- cave ( still in progress!). The attic area is too hot in the summer months and will eventually breakdown & destroy items stored there as I learned. My component boxes were the first items to get a new home!
My boxes go in the attic. I’ve never had problems with them degrading and I’ve lived in very humid and hot environments. Recently sold some speakers and the originals boxes were stored in the attic for nearly 14 years.
Same quandary here as well. We are prepping our home for sale. I have accumulated 80+ cartons for audio equipment! Slowly but surely the number is decreasing.
I still have my original Linn Sondek LP 12 carton, a bit the worse for wear at 45 years. 
I’ve noticed silverfish in the past loving the cardboard. What Ive done in some cases is use some diatomaceous earth earth in boxes I have the are storing magazines . Another take would be to purchase some Timbor (ebay) which is used for termites/insects and make a very very light spray on boxes as you would wood products (its an inorganic salt) …maybe overkill, but in environments w insects, it can be effective.
They certainly do. It’s another reason I seal my boxes in plastic bags, although your treatment recommendations are good ones.
Many of them can be broken down then taped up again when needed.
Probable not with heaver boxes for speakers and some amps though, as many of those are glued or stapled together.
Learned the hard way to save every box. When it was time to sell my beloved Snell Type A III Improved spkrs, I only had 1 huge set of boxes, not 2 sets. Received only half of what I would have because they had to be sold locally to someone who could pick them up.
Here is an idea for condo owners with high ceilings. No attic. No basement (unless we pay for a storage cage). Fortunately, we have 10’ ceilings. In our Master Bathroom, the bathtub and shower are on one side of the main area, and toilet/urinal on the other side. I lowered the ceiling over the left and right sides to 8’ (actually, 5" thick structural shelves) allowing about 1-1/2 feet of storage above, in what we call the west and east attics. Curtain rods allow me to pull 1-1/2’ high drapes across each, so they actually add to the decor and make the 10’ high middle area more dramatic. A couple times a year I bring in a ladder to access them.
Get a bigger boat! 
In ny new house the previous owner built a 16x22 Cedar Room in the basement. All side including floor have cedar boards. 3 Closets are also there. Currently the room is full of my boxes filled with my equipment as I start the build for the new music room this week. Excited.
This is from the realtor pics
I put the expensive stuff in the closets. Lots more in the room now.
This will be my space for the new room
One occasionally needs them for warranty service or upgrades. I keep them all in the attic.
Nice. Insulated subfloor over the concrete?
Yeah its those 2’x2’ 3/4" OSB glued to plastic layer that has many feet. Sell at home depot and lowes. the previous owner did the whole basement in them. Saved me a bunch of work. its nice and dry.
Using SonoPan under the sheet rock for sound proofing. I want to be able to be loud and not bother people or get those calls on the phone “what are you doing down there”