I'm glad he's not a "baby"- he should adapt better, & also the 40 gal. tank won't seem quite so cavernous to him - but do keep in mind that even for adult snakes, new enclosures are disorienting. His fasting probably was due to winter, &/or maybe his home was also too cool even before he came to live with you.

You probably know (but in case you don't) the best time to offer food to a BP is evening/night hours- when they're normally active. Also bear in mind they're "ambush predators", so many have more success feeding their BPs when they're peeking out of their hide in the evening hours- as that's their normal way of "hunting"- not actively searching the way some other snakes do. They like to feel "safe" with nothing sneaking up on them, so looking out of their hiding place for passing prey is the way they stay safe from other things that would happily prey on them. It's usually a waste of time, effort & prey to offer their meals when the snake is actively cruising their home.

Also, never handle a snake before feeding them because it's slightly intimidating to them* & may ruin their appetite. *Think of it this way- the only thing that picks up a snake in the wild is a predator about to eat them. And even when they're captive pets, they still rely on their instincts.

This snake "should" be eating about every 2 weeks (assuming he's of normal weight- not underweight) & I commend you for only offering every 2-3 weeks- offering too often just stresses them out & makes them more likely to refuse. Try not to worry too much- they're quite good at fasting- be patient.

One reason (besides winter) that BPs may fast, especially male BPs, is that when they do eat, they're being fed prey that's too large- so it takes longer for them to want to eat again. Most find that adult male BPs do best on small rats (or mice of equivalent size/weight). Quite a few find their BPs fasting more when they've been fed too much (medium rats or larger). The female BPs will eat more than males (they also grow larger), & may be fine on medium rats, but male BPs stay smaller.