Hi Simon ..yup I believe it is fine. My Quicksilver SIB is now thirteen years old and has been stored in that fashion all those years and I wont be doing anything different for the next ten years or so.
Some pointers .. jack the trailer tyres up so they are not sitting on the ground.. this helps preserve the trailer tyres.
Let a bit of air out the tubes so if we get a high pressure spell..the tubes don't over stretch.
I keep the back of the tarpaulin lifted off the transom so air can circulate inside. The cover is long enough so rain cant get in)It saves dampness collecting. Build a "ridge pole" along the length of the boat with something like an oar or in my case..an old plastic drain pipe. This forms a tent ridge to the tarpaulin so water doesn't collect in pools on the trap.
Leave the bung out in case the tarp get a hole and you don't notice. That's what will destroy a floor ..if rain fills up and covers the floor boards. Ali ones wont matter so much ? but mine are wooden ..so I don't take risks..the bung is out
Hope that helps some