The RH side of a Mk3 is a pain however with the lowered structure for the non-perky butt on the Mk4 it's all but impossible.
My solution was was to use 1/2" long 7/16-14 bolts from the tank side threaded into coupler nuts:
There are no sleeves on the inside. Instead I used all thread. After putting it thru the body but before threading it into the coupler I put a fender washer then a nut on it---the washer winds up against the inside of the body and the nut is between it and the coupler. After the all thread was snugged into the coupler the "floating" nuts and washers were used in conjunction with the sleeves on the outside to adjust the rear valance in or out as needed to meet the lower edge of the trunk lid. Afterwards with it positioned and locked down I cut off the excess all thread and installed the quick jacks with chrome acorn nuts & chrome washers. Although you really had to stick your head inside to see it the coupler nut plus a couple of inches of all thread remained visible:
I simply covered the whole works with a piece of wire harness split loom:
Nothing fancy, just hardware store all thread, couplers, nuts & washers. Simple---cheap---easy