This is an individual decision. It's pretty easy to compare price. Shop for salt shields, compare to price of fabrication materials and whatever you value your time at. Takes 15 minutes to bolt on a plastic one that will be a perfect molded fit for the application...in my opinion just buying one will be hard to beat unless you desire something custom that is not available.

That said I believe they are of very minimal value. Even with shield the sled still gets soaked in salt spray and sand/slush, and the shields can be a pain to work around when doing tie-downs. So my honest advice is to delay, save up more money, and simply purchase an enclosed trailer and sell yours to get the sleds fully out of the elements. This eliminates even the need for covers, and keeps the value of your sleds higher because of the perfect protection they offer. Over time a reasonably priced enclosed trailer honestly does pay for itself by eliminating cover costs, and a certain amount of depreciation and towing damage and corrosion issues to the sleds.

If you're on a tight budget don't look past steel framed (non-snowmobile) cargo trailers with a rear ramp door. Not sure your location, but in many places they are very economical and fully functional, especially if you're looking thru the used market. Plus any older tilt aluminum trailer (I'm assuming it's aluminum?) is on borrowed time and you may be dealing with a cracked frame at the axle sooner than you realize. The aluminum fatigues and will suddenly crack all at once with zero warning on a good bump....risk of this is quite high by the time the trailer reaches 10 years old or more. Many of us have lived that and it kinda sucks. So there are 2 reasons to sell and get your money out of it before that happens.

 

Unless money is an issue, forget the salt shield and cap it. Soooo much nicer not messing with frozen covers. I went from flat trailer, to a slush guard to a cap then sold it for an inline.

 

Unless you are good with metal, I'd just buy one.

Triton makes one and Caliber makes a plastic/molded one. I have seen some for sale, used, on Craigslist.

If I had an open trailer that did not have a shield, I'd get one as it helps keep a LOT of stuff from getting onto whatever one is trailering.

 

I used a salt shield for years on my trailer and it kept the sleds way cleaner than without it.

It is a good inexpensive way to go if you cannot "get" or "have" the room for an enclosed trailer.

As far as "fabrication" or "buying" one. That is up to you and your skill level. Cheaper to build your own for sure.