Are these worth getting for riding in the sand? I had a problem last time that my
One machine blew up from sucking in sand. Should this mitigate that problem?

This is what I did. I also recommend pantyhose to cover the prefilters. cheap and disposable.

I do not recommend K&N fabric filters, if you do a search you see that many others are in agreement, use a foam filter with sticky oil like FFT, I then use filter skins, they get dirty but catch 80% of the sand before it gets to the foam filter, you can change those out if needed, and finally do some sort of pre-filter as shown, for mine I did use a fabric filter, I didn't even bother to oil that one, mostly just used to keep out the bigger stuff and knock it down before getting to the inside filter.
Those pre-filter socks I'm sure help but I have found they would let the fine stuff in and not let it out.

Where would I buy the filter skins?

Yeah what Kuma and rmesser said,K&N sucks for keeping out sand.I think most people run the 2 stage uni filter with the sticky oil,and some run the prefilter like Kuma said.The K&N would probably be ok just to use as your prefilter but that's about it.
https://www.ebay.com/itm/UNI-Air-Filter ... SwvFpbfjvM

I have a oiled foam filter now, is there a cover I can buy or a filter net I can buy as an added layer of protection.

Are you running an airbox? If so you shouldn't need an outerwear.I know they make these but I don't know if unifilters are designed for these to be worn over them.
https://www.denniskirk.com/outerwears/u ... gI6SvD_BwE

Yes my set up is 100% stock

I would still use a filter skin on the foam filter.
it's funny that the Spammer located the post about the K&N Filters that hoser started :)

What's a filter skin? Like the outerwear I posted link to?

http://www.pcracingusa.com/FilterSkins_c_18.html
I usually oil them with K&N fabric filter oil, they do get dirty, but you can easily swap them out or even put it off knock the sand off and reinstall.
I desert racing friend of mine showed them to me, there is a way you can stack them in layers and have a string coming out of the airbox and during a race you can pull off the dirty top layer, I've never done that myself

Well you learn something new everyday
I have never seen or heard of those before