My 2000 came equipped w/monitors. I don't know if that's the same as the '98's. Mine's 19 yrs old now and getting pretty tired. This fall maybe it's last run along the coast from San Diego to Washington state.I have a 1995 northstar that's in worse shape than that one. Try pushing on the ceiling and make sure it it's squishy as I've heard that sometimes that happens. Mine doesn't leak even as old as it is but I've heard from another northstar owner to check for that. You can also pull be mattress and cushions up and see if it ever has leaked in the past.
If you get it, definitely install a CO alarm. The heat exchanger in my furnace cracked about 3 years after I bought it and it was pumping CO gas into the camper... glad I had a CO monitor.