You're gonna get 50 ways to do this.
For me I went the cheapest way I could. Went to junk yard / auto salvage and bought RIBBED truck bed liners $15 each. Cut up and used as guide rails for sled tracks. Screwed them into trailer frame through plywood floor with zinc coated self taping screws.
For the plywood floor took marine fiberglass , 2 part makes 1.5 gallons.
First coat I diluted it with spirits so it would soak into the wood making it "fiberglass". Got some washed sand ($6 a bag) mixed together with fiberglass for second coat creating a non slip surface.
Did a 20 foot trailer for under $150 bucks. Coated the inside AND underneath with fiberglass and still have some fiberglass left over. No rust no corrossion no slip no problem.
You can take the scraps of the bed liner and use then as steps / traction for the sled track between the rails.
To fasten the sleds to the floor I bought E-TRACK rails ... same as used in commercial trailers. $10 for 5 feet. They hold 50,000 pounds before breaking. Only have then screwed into frame so the are probably able to hold a ton or two of load with SS screws.