Having the 7-5 (nflv-skeletal-adapter-75-5-1.cfg) and 5-3.75 (nflv-skeletal-adapter-5-375-1.cfg) skeletal adapters default to empty creates an issue where the maximum capacity is removed, but the fuel as defined in the original config file remains. This issue fixes itself if you switch meshes, but an unsuspecting user may wonder why adding the truss adds 60 tons to their vessel. I think the quick solution may be to declare the Tanks subtype as the defaultSubtypePriority.

Still need to investigate and sort this out.

This may be more helpful

Should note that this is not an issue with Cryotanks installed, so may only affect a small subset of users who don't use the full suite of NF parts.

That is weird, I'll look into it.

My guess is that in the part config you define fuel resources, but the B9PS defaults to the structure-only. That is different than how you approached the Mark IV fuselage parts in which you defined the basevolume in the B9 config, but did not define any fuel resources in the main part. Think the reason that Cryotanks fixes the issue is that the TankSwitcher config goes through and deletes all the original resources.