I am sure this has been asked, I am not looking for reasons behind your answers necessarily, I'll get to that later...

Have an 84 C10 truck, doing some filler in jambs and back of cab and etc, took down to metal then used filler....

Question is... What kind of primer with a decent amount of bare metal exposed?
2K urethane, epoxy, or high build?
Will likely take most of cab to metal

This question comes up a lot. There's a measure of fact and opinion anytime we discuss it.

There is no denying that epoxy is the best adhering, least porous material you can apply to bare metal. However, in my opinion, many newbies think they need it and they don't.

Car sitting in a garage with no chance of moisture getting to it - a good 2K DTM primer is fine for what you are doing. Can't hurt using epoxy but remember that it will need to be sanded again later if you are going to shoot build primer or color over it. 2K DTM will also need to be sanded, but it is a lot easier to sand. Some epoxies go as far as stating they are "non-sanding", in their tech sheet - so make sure you look at that before you decide.

Generally epoxy is not "high build". Most 2K urethane primers are.

What about polyester primer?

Also, is the Clausen all you need primer liked or used by many? Or mostly hype?

I tend to agree with chris, inasmuch that there seems to be a tendency to use too many products in a lot of repair/restoration jobs. Because my shop is primarily a 'production' type environment we don't have the time to go through a lot of the processes that are commonly discussed here. What that means is that bodywork needs to be straight before paint so that all that is required is priming and topcoats. Clear needs to be good enough 'off the gun' rather than having to need wetsanding. In between, the minimum number of processes, because every one adds time and we don't get paid for that.

So, a good DTM primer is the solution for us. Provides more than adequate protection unless the vehicle is going to see severe service conditions. Home restorations are obviously different but the concept of keeping total film build low needs to be borne in mind there too. The more layers that you put on a surface the higher the possibility that it will fail. If you introduce different chemical compositions as well then that propensity for failure increases at logarithmic scale levels.

Polyester. Generally as spray bog. Cheap and nasty solution for inadequate bodywork in my opinion. But, is used sometimes as a quick fix for wavy side panels. Hammer it on then level down quickly with a long sanding board. Almost guaranteed to crack and craze with just the slightest knock or, after a few years, just temperature variations.

Non sanding epoxy. A lot of epoxies can be made 'non sanding' with a different mix of hardener or sometimes reducer. What this means is that they can be overcoated before they are completely cured. 'Wet on wet' the process is generally called and can be achieved because the thinned epoxy lays down very flat and smooth. Your booth and job needs to be ultra clean so there are no dust nibs in the epoxy, which will show through later. It doesn't mean that you can't sand it - you can. Just need to wait the longer time until fully cured.

'All you need' primers. Basically a DTM high build primer aimed at the non-professional. All the paint manufacturers have them and they're usually cheaper. Good, single step solution, as I mentioned above.