Obviously was an old boat trailer to start with. Cut the pads and perches off and ground them smooth. Added 1 1/2" angle iron across the front and rear for the lumber to sit in. Flipped some angle iron over and welded equally spaced to support the lumber.

Once in place I bolted the lumber down with stove bolts and nyloc nuts. Hard to see but had to notch the lumber to clear the curved cross beams on the outside edges.

Got some pivot tie down loops at Tractor Supply and welded 4 sets per side evenly spaced

It became clear very quickly that the floor was not long enough so I added more angle iron and two more boards crossways. The side parts of the trailer curved forward where I added them so had to trim the ends of the boards to fit but was no big deal. I then added the rock guard panel in front of that.

I made a mount toward the front to put my packer box on and we carry the helmets, tools, straps, etc. in it. Also added a mount for the spare tire as seen here. Hope this helps anyone wanting to convert a boat trailer into a utility trailer. Remember that it is tongue heavy so keep the weight evenly distributed. When I haul one ATV I strap it towards the back of the trailer. 

Here you can see the ramps. They are 10' long. Bought the bolt on aluminum ramp kit to put on the ends of the lumber. Not the fanciest but you do what you have to on a budget. I eventually want to mount them underneath but for now just slide them under the ATV's with a strap across the top.