my '05 job
I installed a PDM60 on my '05 GS a few years back (documented here). I never used frame grounding. I ran all of my accessories to ground back to a dedicated ground bus bar tied to the PDM ground. The bike is small enough to run these easily. I do recommend pulling the tank to make the wiring cleaner. I don't expect your '08 is any harder than my '05 - which is very easy to do.
Good luck....Post pics!!!
'05 BMW 1200GS '09 Honda CRF230 '10 Yamaha TW200 '07 KTM 400 XCW/EXC '15 Jialing 150 GY2