Those lamps are a bit of a chore to move around for sure. Especially in a cluttered garage like mine, or up/down stairs that turn 90 degrees partway up. As for transport, a youtube friend told me a story of having a case of newer Alto slimlines go flying off the bed of his pickup truck at freeway speed! (Hey, another reason for me to look into buying one of...those.) Just gotta be SUPER careful! But yeah they're a bit of a pain. I laughed reading "knocking 2' off a lamp".
If you REALLY want a SL, I think you could still go to Home Depot or Lowes and buy a F96 striplight, albeit a cheap modern one with an electronic ballast. I almost did that a couple years ago, just to have a slimline. If not, and you find an older (even 90s-00s like mine) one, GET IT! They seem hard to store, but they're not THAT bad just leaning up in the corner! (That's how I'm using one of mine). But if your grandpa's shop sells yeah grab that HO there for sure! (And a SL at the same time). You'll be glad you did 30 years from now LOL.
I'd probably install my 8ft slimlines in my garage when I get lamps, or in my storage loft. If we move out of this house though (Either building a new, nicer one on the same lot, or moving someplace else) I'll probably take as many of my fixtures with me as I can, though for a new house I wouldn't want used fixtures honestly...everything electrical would be brand-new. But I'd stick my used fixtures in an outbuilding or something...