Flights returning to the USA and customs

[qwerty]

I've been flying to Mexico and have got a couple questions.

Upon returning to the USA from mexico which is usually very VFR, my destination is mostly IFR because of the a weak marine layer. At times this marine layer could cause me not to get into the airport with customs and the next closest airport with customs is an hour away.

My main customs airport has a vor approach with high mins and another airport with in 5 minutes away with an ILS that would make a great alternate (no customs)

So, for IFR back into the USA, does my required alt per part 91 must have customs as well?

thanks