I thought it was neat. It was quite a sight to see all those people standing in snow at the side of the highway offering mass.
I thought they are not supposed to do that without the Bishop's permission, and the altar should be stone I think. That's the legalistic part of me.
Then I thought surely God would be pleased anyway. And how did I know but what they got emergency permission via cell phone. Or maybe it doesn't matter any more; it's been awhile.
How many Masses have been said on the hood of a Jeep? How many consecrated hosts were exposed to snow, mud, volcanic ash and other garbage? The men who were about to do battle and possibly give their lives didn’t worry about such things as permission. They were in the cathedral of heroes.
Those are not required for "battlefield conditions," and I think we'd all agree those folks qualified. (See the Don Camillo books for examples--and some hilarious stories.)
There are portable wooden altars for just these situations, beautifully made. We had a priest come offer the traditional Latin Mass at our fathers-and-sons campout. We built a canopy out of a huge tarp and some wooden stakes. About 60 of us, 6 altar boys with vestments and candles. Yes, it was awesome.