Are you considering a modem because of lack of stations available, or
to be able to do your internet under way, or some other reason?

Yes.

When there's no signal it'd be nice to be able use the cell network service.
No sense bothering with using that if I can get wifi. I'd like to have the
option.

That and as you've discovered, if you're "too close" to the base station it
can be tricky to get a reliable connection when the antenna's pattern
"misses" it.