When I just had one kart and a scissor stand I built two work shelves (3/4 ply bookcase style) on either side of the trailer – the same height as the kart stand. Push the kart in on the x-stand and roll it right onto the shelves where there are 4 d-ring tie downs. when the kart wasnt in the trailer I bolted my vice and tire changer to the shelf. The shelves we’re also installed with loose pin hinges so they could be removed and put in my garage in the Winter when we weren’t racing.
if you’d like a picture just email me at email@example.com and I’ll send you a picture of the trailer with no kart in it back then.