I use Bike Pro removable chocks. I have two chocks and 6 mounting plates. 2 plates in the Cyclone, 3 in my motorcycle trailer and one for the house garage.
The plates bolt to the floor. The chocks then use two bolts to secure to the plates.
There is no under belly to remove under the garage for access.
I had to loosen my fuel tanks to get a wrench in the area I mounted my chocks.
The factory supplied tie down "d-rings" use self tappers into steel channel under the floor. The floor is 1" thick plywood if you decide to just screw into the floor.
So when you look in your garage, everywhere you see a factory installed d-ring there is a steel channel going cross wise under the floor.
I will be installing aluminum load track this year, my preferred tie down method. I will probably have a mix of using though bolts into the steel channel and the same in the plywood.
The tough part will be adding tie downs near the side wall, there is no access and the walls are thick enough that you will not be able to use self tappers into the length wise steel frame rails.
I don't have a better picture, but this is my bike trailer.