Hi Crimsonstardust,
I dont have any videos to provide, but since you know what it means to play back on paper, maybe these are some recommendations for good back units, so here it goes. Of course this is all in my opinion.
Most obvious would be Cheridum, but you really need tp nail those snipes well, which can be hard, as you need to predict their landings. It has shield bits, which can provide amazing protection for your teammate. It also has bits to send out to harrass so you can land your snipe shot if they hit by a bit. It might be difficult to play back as Cheridum with its high cost because players may decide to focus on you quickly to overcost the front unit. Overall if you can pull it off, its very rewarding and any front unit would love the support from a good Cheridum.
For a unit with less cost, my preference is GP-01. GP-01 is a pretty fast unit with a lot of cancel routes. This is valuable for a back unit as you can jump in and out of engagements quickly and safely. The twirl ( I think its 4BC or 6BC) is another really good evasive method if yoi have boost. One other part where I think it excels at is the charge shot A. The CsA is a fast knockdown which deals ~120. The awesome part is that its actually a pretty fast beam shot and if the opponent is not paying attention to you, its pretty eaay to hit.
As for 1000 unit, maybe not so back unit, but I think Arios is pretty good. Arios, similar to GP-01 is fast, and can quickly get in and out of situations ( although with a lot less boost ). Arios has a wide range angle for his main, usually only need to land your A twice to down an opponent as you dont need to zunda often because your assist will often shoot a shot with you, leaving you with boost to avoid incoming attacks. I personally found Arios a great unit to support with its versitility.
Above are just a quick few of my personal opinions and favored playstyle. Others may criticize me for those suggestions, but they certainly work well with me when I play!