Heat lamps, aka incandescent lightbulbs, are a cheap way to heat a neck. I fixed by bandmate's Paris Swing GG-42 Gypsy Jazz Guitar that was left in a closet facing south, during the whole summer of 2018 -- in a thin-walled mobile home. The whole top/neck joint area had slipped, causing the guitar to be unplayable. A couple of days with a 100-watt lightbulb inside, and clamped to the workbench at each end of the guitar. Then let it cool for 24 hours. Worked like a charm! Better than waiting until the next summer, clamping it up, putting back into the closet for three months, and hoping for the best. It would be a bit more difficult to contain the heat from a lightbulb when straightening a neck, but certainly doable. I've used compression fretting, as Dan Erlewine shows in the StewMac book, Fret Work -- Step-By-Step. It was an old classical someone gave to me and it had a warped neck. I thought it was a beater so tossed into a corner for 10 years. Then I took a closer look. It was a Salamanca, built in postwar Germany in 1949, had a solid Engelmann Spruce top and was light as a feather. It needed a refret so, the compression method made sense. I ended up selling it in 2019 for $800. One oddity was the non-standard spacing for the tuning machines. The originals were junk, so I used individual classical tuning machines. A gap at the 14th fret, that was about 5/16", wound up at 1/10" (straight edge sitting on the bridge and nut) -- not too bad! The neck is strong, hard maple with a square profile -- the stiffest neck I've ever seen. The hot closet had no effect on it. My friend uses 10-44 D'Addario Gypsy Jazz strings, so not too much tension on the neck -- even though the scale length is 26.4".