Bad idea putting this inside radio.
Mike
I agree 100% first it is a bad idea to ever put an amp inside of a radio!
Another moronic thing to do is putting an amp from the factor on the bottom of the radio to heat soak all the parts above.
Put the amp away from the radio. First this will allow you have a proper heat sink not just a slab of aluminum. No way anything that will fit into a radio has enough means to dissipate the heat of 100watts in spite of the idiotic stingers with exactly that design!
You might as well take the radiator out of 4cyl Toyota Camry and attempt to use it to cool a 1 Ton Dodge with a Cummins in it! At least that is a radiator of proper design just the wrong size. Maybe this has escaped your attention but air cooled devices like Motorcycle engines, old light aviation engines, old Volkswagen engines all have fins not just a mass of aluminum or they would have just added more aluminum to the blocks and dispensed with the fins if that was possible.
You need to have as much surface area as you can exposed to circulating air that is what the fins do. If you you just end up with an aluminum oven element inside your radio radiating heat from the transistors back into the radio. Even those Moron at ranger and those Chinese radio's with way more power than they should have put the heat sink on the outside of the radio and cast fins in even if they are terrible fins.
Put that thing in a box away from the radio with a PROPER so not cheap heat sink. Do not put it in the glove box or under a seat it needs to have plenty of air flow. Heat sinks should always face up even though moron companies design them often so the switches can only be read with the amp upside down.
The first time I saw a radio with an amp built under it or with out external heat sinks I based them for being stupid that has not changed in the last 20 years. Even those poorly designed RF Unlimited DX and Later FX kits put the amp outside the radio on the back and had a real if too small heat sink! Later they came with fans or the provision to easily mount fans.
I do not get it why do people insist on putting the amp inside the radio. What good and practical purpose is serve?
Like Nancy Reagan used to say "Just say no!"
LOL....Good Luck.....Remember....Friends dont let friends mount an amp with improper heat sink in the radio!