Do I need an IRP cab card for non commercial use?

Doesn't matter. My uncle had a three axle truck he used just to go get hay for his horses. Registered as a regular truck or farm truck and had "not for hire" on the side. Still had to buy fuel permit for the third axle. If you only have two axles you're exempt from the fuel permit requirement.

 

No. A Cab Card is another name for an Apportioned Registration, Your not using your truck for commercial purposes so none of that applies.

From the horses mouth http://www.irponline.org

Who is required to register under the International Registration Plan (IRP)?

Any carrier that has a combined gross vehicle weight of at least 26,001 pounds or more with two or more axles, who intends to travel in two or more Member Jurisdictions (crossing state lines) transporting passengers or goods is required to register as an Apportioned Vehicle with the IRP.

 

I don't even think you can apply for apportioned tags (IRP) without a USDOT number and IFTA registration.

You shouldn't be any different that a 3 axle motor home. Be prepared to get hassled by cops and for bypassing the scales though because you are going to look like a regular commercial truck. You also can't make a dime from appearances or things like that or everything changes.

 

Those rvs that have not for hire and/or ifp sticker on them are rvs that are registered under a company name not under a person. A lot of people do that for tax reasons.