Red-dyed "reefer" diesel?

It isn't just the Feds that test diesel fuel. State tax agencies may also test.
They will/can test ANY diesel fueled vehicle if they choose to do so. If they find traces of red dye, they can and will assess the penalties.
They can do the same for ANY "special fuel" vehicle. If your vehicle runs on propane or CNG, you MUST pay the highway fuel taxes on all the fuel you use. If you convert your diesel to run on home-blended bio fuel (used fryer oil), you MUST pay the highway fuel taxes on every gallon you make! If you work at an airport, and have access to waste jet fuel, and burn it in your on-highway diesel vehicle, you MUST pay the highway fuel taxes on every gallon you use!
Will they catch you if you don't pay the taxes? Maybe not. How lucky do you feel?

I have personally observed and had my pickup tank dipped at roadblocks in Texas, Nevada and Arizona. So, NO, it is not JUST 18 wheelers that get their tanks dipped. The lineup on I-80 west of Reno was over 100 diesel vehicles waiting to be checked and the MAJORITY were not 18 wheelers. The extreme fines they have for this violation are NOT worth the few pennies you save.

The problem would be how they apply the fine. If your vehicle gets tested and has any noticeable red dye your fine is based on tank size not how much is in your tank. The fine is very expensive. A truck driver near us in WY got caught and the fine was several thousand dollars.

Never heard of a motorhome getting stopped for a fuel check.

Never heard of anyone other that my aunt's third sister- in- laws, husbands brothers son who got caught. I think he is still in prison.

When I was using Red Dyed Fuel in our ambulances (with exempt plates), the Ford Dealer said he had to report finding Red Dyed Fuel in our system, he backed off when I pointed out that we were exempt. So they will find you somehow... they want your money. JH

Around here they will dip any tank, not just commercial.
Dealerships have been fined heavily just for having used vehicles on the lot that a previous owner has used red diesel in.
So some dealers will dip a tank upon trade in and if it comes up red, they will not take the trade.
And it takes very little to test positive. My mechanic friend says he has a customer that had run several tanks of normal fuel through the engine after using just a small amount of red but still came up positive and was fined.
A dealer will also void the engine warranty if they find red.
All in all it just isn't worth it.

I don't think it matters who gets tested. If you get seen doing that.. big fines.

It is still cheating and dishonest.

I think the Internal Revenue Service will disagree about only 18 wheelers being tested.