Recreational vehicle repair. Sales are way up since the industry almost died after 2007/2008, and the manufacturers are producing crap quality in order to satisfy sales demand. It's not uncommon for someone to spend $400k on a new RV and have to take their new purchase back for a months worth of rework -- only to find out there's no service openings for 5 months. What's stopping me is the up-front capital requirement…
One interesting sub-niche of this is RV solar installation, this seems to be booming as well with few who know how to do it right. AMSolar is the premier one and are booked solid months out.