The plans on most tandem RV’s call for nutplates for the forward cockpit floor area, and pop rivets for the aft section - at least all of mine have, including both RV4’s. There is nothing wrong with using nutplates for the aft section too, and many have, although I have not needed that for maintenance. I have manual flaps on my current RV4 where everything is above ‘sea level’, but I had the electric flaps on my last RV4, and had to change my flap motor. Removable aft floor would not have made any difference. I was able to access the motor and all mechanical components with the aft floors riveted in place. One area to look at is the side wall angles where the floor attaches. This piece of angle is 1/2” wide. Make sure you will be able to drill the holes (nutplate jig) in that area. Then you will be installing the rivets in the nutplates. A squeezer may not fit in that confined area. Shooting the rivets might require an offset flush set. At the rear end of the floor where the seatbelt clevis is, not sure you could get a nutplate in that area. It can be done, and has, but there’s some obstacles you’ll have to deal with. Might be worth it if you have maintenance issues to deal with under those aft floors.