If you must choose between an aquarium and a tub - I would recommend a tub.
Glass is difficult to control, or rather, the factors associated with it are. Boas do not enjoy overhead lighting (heat-lamps are a great asset when using glass, but are all around more suitable for an arid reptile, such as a King Snake, desert gecko or Bearded Dragon. Lamps also dissipate available humidity much more quickly, and in an open-air enclosure, this can prove quite detrimental), nor being exposed on every side (as you've presumed could be a problem).
Something like this would be appropriate for a young BCC.
That setup is a 75g aquarium personally designed by me. The screen-lid is a custom refitted one (hot-glued a piece of plexi-glass 1/3 the total size of the lid beneath the rim to minimize humidity and heat escape as well as the usual "nose rubbin" tendency displayed by some snakes kept in aquaria.
That setup ran me over $500 and houses a 4 foot female BCI. She will by summer's end be placed in a T25 produced by Animal Plastics.
If you spend the money - which can be a considerable amount - work out the kinks and tune what works best for your snake and less for you, you can make an aquarium work. Every problem associated with aquarium usage is void when applied to my series of setups, and I am proud to boast a year running without a single incomplete shed.
Get a tub. It's easier.
