It is a rule, but I've never seen it enforced at Div 2 LODRS races. From what I understand this rule applies to generator units that you might say are permenatly mounted in a motorhome or enclosed trailer. I don't think they are too concerned with portable units that can be moved around.
Camping World sells a bolt-on type of exhaust pipe extention called a Gen-turi. It cost somewhere around $150 if I remember correctly. I made my own simular exhaust extention for my motorhome for about $30. If you go to a web site called rv.net and do a search of the forums for "homemade gen-turi" you will find pictures of what others have made themselves and descriptions of the parts they used.
Hey Dan Moore, you're #1.
RIP Mark Graham