The 454 is a fine engine (if maintained properly) and was used successfully for many years in large trucks and motorhomes. It was replaced in the early 2000's in Chevrolet-based motorhomes with the 8.1L engine on the Workhorse chassis. The Ford equivalent was the 460, replaced by the newer Ford V-10 around that same timeframe.
40k miles seems fine, but find out the details on those miles. It's better to have a motorhome that's been used and maintained regularly throughout its life (even if that means higher miles), versus one that was driven a lot in its first few years and then sat unused for the next decade in a driveway/field/yard/barn. Rubber/flexible parts and engine fluids do not like sitting cold and still, and have a higher chance of failure if/when thrown back into full service after long periods of non-use.
I tried to run a pricing estimate for you on www.NADAguides.com (click RV and follow the prompts, do not add any "Options" for used RV's) but the Brave 29RQ doesn't show as a 2001 model. In fact all the 2000-2001 Chevy models on NADA were Workhorse, and would not have had the 454. It looks like 1999 was the last year using that engine, which matches Chevy/GMC pickups and Suburbans also. According to NADA, the Brave 29RQ was last made in 1997.
You better do some checking on the actual model year of this rig, which follows the year the truck chassis was built (often a year or two older than the motorhome body).