If the floor is structural, you really need to support it to keep the integrity. Do not rely on the trailer with it sitting on the axles, you need to jack stand the trailer flat on four corners and block the boat on the trailer frame. The hull can twist and contort and do all sorts of weird chit otherwise...
I have only done one tunnel and it was no all that different from doing a vee hull, just more things to take into account.
Good luck.
GT