I went with the thread that Newty posted, I know someone else did it too but I could never get their pics to download on my computer, for some reason I can't always get the attachments included in some threads. I got the Bass Pro seat swivel for 9.99 ( I'll see how it holds up), I got a 5/16" aluminum plate 9"x13" at Metal by the foot and 1" angle cut 9" long, costing $30. I used a cheap poly cutting board that I got at Walmart for $3, I cut that to match swivel and took Newty's advice and cut another piece to double up the spacing. I think the cutting board was 5/16" thick. I got all bolts and nuts at Lowe's, The screws that go into boat seat attaching 2 pieces of cutting board and swivel are 1/4-20x 1 1/2" and are perfect once you tighten 'em down with driver- if you screw in by hand they appear too long. Step by step goes like this: 1- remove seat cushion and remove seat.
2-cut the cuting board(2) and attach them and swivel to seat, I used the 4 center holes in seat, with 4 sets it gives you a few options to play with.
3- drill holes in plate and attach it to slide rail ( I centered mine)- leave out all 4 poly spacers that were originally there and place 1" angle just forward of the back bolts
4- place the seat and swivel assembly on plate and play with positioning until you get it where you like, then mark and drill holes in the plate
5- attach the plate to the seat assembly
6- attach that entire assembly to the slide rail
7- get a cold brew, swivel around, kick feet up on rear seat and take a drink or more
Parts list: 5/16" aluminum plate 9"x13"
1" angle aluminum 9" long
seat swivel- most will work just chek bolt pattern on seat bottom (mine is 5x5)
cutting board
4- 1/4-20x1 1/2" machine screw and washers to attach swivel and cutting board to seat
4- 1/4x1" carriage bolt and washers to attach swivel to plate
2- carriage bolts original diameter as front 2 in slide rail but you need them 1 1/4" long
I think that's got it, if I left something out let me know. Pics should help.