I would use the missing service records to my advantage and get the price down which I did when I bought my coach. Didn't have anything from the prior owners including all the owners manuals. The hazard of a repo. Since you don't know when the fuel filters were replaced last you'll have that immediate expense, air compressor dehydrator service, engine coolant change and such. All will need attention as soon as you take the rig home, presuming you do buy. The chassis inspection will help to confirm the need for post sale work.
Concerning the Car Fax, I pulled one when I was negotiating to buy my coach. Showed the initial sale and registration, all registration renewals, repossession, bank auction and such. Also listed the locations and dates when all the events occurred. No records of maintenance, warranty work or accidents but I suspect this is due to RV service centers not participating in the data base program.