Cabinet build

1) 1,950 watts is going to draw 17.73 amps on 110v AC.  That will not work on a 15amp house circuit.  It will work on a 20 amp circuit, so make sure where you want to put the smoker will have the proper power available. 

2) 4x4x8' is a lot of air space to heat up.  How much meat do you anticipate smoking at a time? If you are not smoking a dozen pork butts or briskets at a time, then I would make the cabinet smaller. Less air volume to heat would be much more efficient. Now on the other hand if you are going to be smoking a ton of meat at the same time, then you need to go higher on wattage and change to 220v to handle the load.  Remember all that meat is going to be cold, cold, cold when first put in.  If you are putting  dozen (or more) butts in cold it will take forever to recover the heat drop from that cold mass of meat being put in the pit.  I would definitely size the cabinet for the expected meat load and then do the same with the heating element (or elements if it's a lot of meat).  Insulation helps, but size of smoker cabinet and meat mass do matter.

Also a lot of all wood smoke houses have been made using 2x4's for the framing. I would think that is much less expensive than square tubing and easier to work with as you don't have to drill and bolt into the tubing.

If electricity (220v) is not a problem, I would up the ante and run the wiring for 220v.  You could use 2 (or even 4) of those 110v elements you referenced and have a single PID controller switch them.  I would split the 220v into the 2 110v legs (unless you change the elements to 220v elements), and then install a switch in the feed line to each element.  That way you could dial up or back the wattage to suit the load.  You could do the same thing for 220v elements, just don't split the feed.  You could either have a single large SSR or use the one PID to trigger a SSR for each element and put the element selector switch in the low voltage feed from the PID to the individual SSR's.  That's probably the cleanest way to do a multi-switched element cabinet control as it's a lot easier to switch the low voltage than a 20amp load branch.

It should work...

My smoker is 6'x18x30 I have a 1500watt element in it with a pid I have plenty of heat I did a 30# batch of stick the other day it was 5 Deb with 20mph wind it did just fine but if I had to do it again it would be 220 not 110