Straight talk can be either Verizon or ATT tower based, they have contracts with both companies.
As to tethering or hotspot use, they have never condoned it, but could not tell you were doing it until about a year ago. Now they will shut down your data feed if they are notified by the tower service that you are a hot spot user.
If you want the data strictly for when travelling, you may want to buy a connected car device and use that for months you are travelling.
Connected carOr switch to an unlimited data Verizon phone plan.