Skyler,
Putting the BPF on each side of the flat pack should work out ok. Try it and test it out. We have a 6 cavity Wacom duplexer on Badger that has BPF cans on each side of the 4 cavity BpBr duplexer.
Dave Novotny, WA6IFI
Chairman, Cheyenne Mountain Repeater Group
719-439-9077
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Dave Novotny
WA6IFI