thank you for the reply/support! I'm not a paint wizard like you! after thinking this idea over, and watching some other woodworking videos for doing rabbets... my idea has evolved to just a wide board with router mounted at one end, and a strip of 3/4 x 3/4 on the bottom side of the piece at the other. the 3/4 will ride the edge of the 5x5 panel and place my router at 26.5 or 24.5 or 16.5 depending on the cut. not sure that makes it any clearer.
appreciate the input. well, the reach needs to be 26.5 at widest... which is quite wide. most of the store bought rabbet guides max out around 12" afa I know... but if your ryobi goes to 26.5 I would be interested to see it.
the problem with a marker stick... or just drawing a line and putting a fence on it... it's unlikely to be perfectly parallel as you place the fence. the cab construction I'm doing is going to require very precise parallel sides. the sides will be exactly 3/8 larger on each edge of the baffle, for instance, so they slot into a rabbet cut into all 4 panels. If this isn't perfectly square it's going to cause assembly problems. with a table saw or panel saw this would be trivial... just need the sm parallel precision with a router. actually was thinking a lot about getting a router panel saw setup... but just do not have the room.
EDIT: I should say that's a "Dado Joint" for the baffle... as rabbet is only at edge.
thank you for the thought - that could certainly work, but planning to place the 5x5 on the garage floor and don't have a 5x5 of scrap, and given I will be kneeling on it... don't want to risk flexing.