You don’t need an eld for under 100 air miles whether inter or intrastate, just writing mileage down in a small book is the easiest and cheapest way to take care of it
It’s an easy thing, set up ifta account, through Mississippi, it should be free. Get license and stickers in mail. Put stickers on Truck, keep a copy of License in truck.keep track of miles driven and gallons purchased in each state. Within 30 days of each ending quarter, go online, to Mississippi IFTA efile, fill in the blanks. Pay with credit or debit card. Staple a copy of all fuel receipts, and trip, mileage reports, to a copy of the finished form, for your records, in case you get audited, they may request logs for supporting documents. Miles should match. I doubt you’ll ever get audited.
We travel the vast majority in out home state, I keep up with all miles, but only fill out a "trip log" when going out of state. I've been through a IFTA audit, and they said this was fine.
I guess each state is different, but in TN you'd have to go to apportioned tags. In TN, you don't even have to have a DOT number, if you stay in TN. I envy those intrastate guys, they don't have to do any of the stuff that comes with acquiring a DOT number. No HOS, no drug testing, etc.
Generally, if you operate in two or more states, you need apportioned plates and an IFTA account. If you operate in only one state, you need an intra-state authority.