Thanks for all the comments, guys!
I spent most of yesterday working on the interior, but I did get some stuff done - the quads are mounted (waiting for their ammo boxes) and I added the spares from the kit. I also added a couple of large ammo boxes (technically from a resin minigun kit, but here they're big boxes of 40mm grenades), fuel and water cans and a scratchbuilt box for spare .50 cal barrels:
The antenna, water and fuel cans and the handles on the spare barrel box are all Stryker bits from the leftover sprues that come with the M151 kit.
The interior has instruments from Archer fine Transfers. The scratchbuilt LCD monitor is just a printout of a desert scene pasted onto a standard Protector display. The support arm and many other bits in the
cockpit interior (like the radio's handset and the windshield wiper motors) are also Stryker spare bits from the M151 kit.
The radio is sitting on a box that acts as the Protector's computer. The display/keypad to the right is a resin copy from a DML MRLS kit. If it looks like there are a couple of AT-ATs on the display it's because I used the decal from an old AMT Snowspeeder kit.
I still need some more bits in the interior, then make decals and finish this.