Lost cause? - Paving on decking

[BCooper]

It's bit of a suck air through teeth question this one.. I think I already know the answer.

I inherited a 10 msq timber decking with paving slabs loose fitted using propretry spacers and shims etc. Over time it's got springy as the OSB board underneath finally gave in to damp despite being sealed with what looked like a sheet of visqueen.

I've stripped it all back to joists, reinforced and and added loads more support , re-covered the deck in 22mm marine ply over a breather membrane then fibre glassed over the lot. You could park a truck on it.

The thing is, i'd like to re-lay the slabs but I need to grout or seal them somehow to keep all the gunk out.

Do I:

a/ Use the spacer/shims again or b/ Somehow bond them directly to the fibreglass deck?
c/ Use Polymeric grout? Is it flexible enough?
d/ Use some sort of flexible magic stuff out of a tube?
e/ Give up? (which I think will be the popular answer)

Can't use timber decking - I have to ride my motorcycle across it and any kind of damp will have me straight on my side.

[PavingSuperstore]

Might be a silly question, but is there any reason the paving needs to be suspended above ground level rather than have the more typical Type 1 sub base etc?

[BCooper]

Yes, It's part of the base of a timber workshop, raised because it tends to flood in heavy rain. I could have taken the timber out and poured a concrete base instead I guess, but that means cost plus effort and I'm more of a carpenter than a builder...