Another common hiding spot is the bathroom, check behind the toilet tank and quite often there is a open area under the sink cabinet accessible through a small gap at the top of the kick board.
Two tricks for knowing your snake is still out cruising around....
Flour sprinkled around the baseboards will shown when he pases by. Similar and more real time is stacked up empty soda/beer cans also along the baseboards. They tend to follow solid edges, if it pases by the cans and knocks them over, you could hear them and come out to find the escapee.
BTW, how old is the rainbow boa? Obviously older ones will do better for longer periods at less than optimal conditions.
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Thanks,
Dave Colling

www.rainbows-r-us-reptiles.com
0.1 Wife (WC and still very fiesty)
0.2 kids (CBB, a big part of our selective breeding program)
LOL, to many snakes to list, last count:
26.49 BRB
20.21 BCI
And those are only the breeders 
lots.lots.lots feeder mice and rats 

