i think a groove for the heat tape is alot of extra work for a DIY rack. the groove would be really shallow and u would probably need to build a jig for consistent depth. this is not something i would freehand. i guess u can use dado blades on a table saw as well (but i'm not sure how effective they are at that shallow depth).
that's fine. just as long as u can reach your optimum temps.
just use foil tape: https://www.lowes.com/pd/3M-1-88-in-...C-Tape/4009603 just tape down the sides of the heat tape over the copper part and u should be able to push and pull your tubs in and out seamlessly.