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robow I'll usually double check dish with my $10 Nashbar gauge but that requires taking the wheel off the bike to do so. Vertical hops? Just spin the wheel and they will be revealed against the tape just as they would by a truing stand plate. That said, I've found that vertical roundness is more a function of the rim quality and evenness of initial spoke tension. Not much you can do to correct it later.
If you want to be that fussy about the masking tape lines just apply the tape, measure the distance between each seat stay, mark the center point with a dot and draw the lines 12 mm left and right for a 24 mm rim. Close enuf!
Not as convenient but just as accurate as any Park stand for occasional use. In comparison, the stand in Russ's photo above looks like it was built by Rube Goldberg with its adjustable caliper and all its knobs and springs! Keep in mind the OP said he needs something to use "every ten years or so".
Robow, I've always wondered ... Is Raybo your brother? Ha Ha, just kidding!
edit- if you look at my photo above you will see the back side a fender bolt marking the center point of the bridge.