I have been reading some build alongs about putting reflex into bows by gluing on a backing like hickory.  Many of these mention using a hot box.  Is is necessary to use one?  What are some other options?

No you don't need a hot box. If you use URAC185 glue, just keep the glue up someplace where it's 70 degrees for 24 hours.

I am using Urac185 on my first bow ever tonight it is gluing up right now. So I will let you know how I like it tom. I usually use smooth on but I am like you and don't have a good hot box to use right now or the money to go build one.

Yes you can glue in reflex or deflex as you glue up your bow.  Depending on the glue you use, you may or may not want a hot box to cure the glue.  Smooth-on cures best in a hot box but it is not needed if you have the time and 70-80'  workshop temps.  Urac185 is a wood to wood only glue as is Titebond.  Both of them will cure at room temps. But if your shop is not heated like mine is, a hot box helps in that environment too.

I have a heated shop it stays right at 65-70 degrees in there. When I use smooth on it sets for a minimum of 24 hours before I do anything with it. I did learn the hard way that you should glue the backing and the bow so there is a very good bond. I had a piece of hickory start to come apart during tiller and had to back and steam the whole bow to release glue and start over.

If the temp in my shop is under 70 degrees i put a blanket tent over my form and use a 100 watt bulb for a couple of hours.
Urac is supposed to be good at 65 degrees but it takes forever.
Ron

Thanks for the advice I may have to try that macbow

the foam board with metal glued on makes a nice box, some light bulbs and stick a cheap metal thermometer in the end works.

I know a guy that during glue up actually put the bow & form in his truck with the windows up and parked it in the direct sun (during the summer). It probably got up to 120+ degrees or so according to him, maybe 130. Perhaps not a perfect solution, but it was better than nothing. Just a thought. He used smooth on and never had a problem with that bow.

That said, I do use a hot box.