Two point I have run into. 1st, the underside of a manufactured/mobile home is not considered "inside", so this is ok.
2nd, to install a 100amp service for a 200amp rated home is a violation. The manufacturer wants 200amps, so you have to install it. You could get a letter from the manufacturer oking a 100amp service, but it had better be in writing. There was a case in Colorado where this same type of setup was completed, and there was a fire (not electrical) that totaled the home. Investigators found out about the incorrect service size, and the insurance was cancelled.
As an inspector, without this letter, you cannot ok the installation, per 110.3(B).