Congratulations on doing a great job John!
I love solutions that make use of existing situations and/or materials.
I've been contemplating something that might suit here, but haven't yet settled on anything. Currently the gear (such as as it - very modest beginner stuff) sits in a converted (enclosed) carport along with a couple of motorbikes. It has to be carried out - which is no big deal as it's only a couple of metres.
Initially, I played around with the idea of reversing the usual arrangement - leaving the existing roof in place and building a moveable floor that rolls out instead. It all seemed good on paper but the problem would be getting it as stable as I'd wish. I guess that's Bojan's point about a pier.
However, at this early stage, perfect conditions aren't very high on my list.
Wishing you many happy hours of play in your cubby. It's a beauty.
Cheers,
Chris