Cumminsguy71,
Just make sure your ticket that is signed states the you are making a weather seal weld ONLY! THEN make darn sure it don't leak. Diesel test the seams.

Dwayne,

It's all a matter of how you see the problem.  I see plates over a deep hole, and I have no idea what's traveling over and around that hole.  So my gut instinct is to weld those joints joining the plates together with full penetration welds.  The perimeter around the hole could have a single pass seal weld to hold the plates in place and keep the rain out.  But I'd groove them slightly, just to get a flatter finished bead and to get a stronger weld, on the off chance that some heavier traffic crosses that plate and causes it to flex.  The owner would thank you if that kept the joints from leaking in a year.  I'd probably also suggest they get an engineer to figure out the load rating and paint that on the face of the plates, to make people think about it before they drive a forklift over the hole...

Somebody else said full pene welds would warp the plates.  Probably, but the distortion could be controlled with some temporary strongbacks in place on the face of the welds, and the perimeter welds completed or at least tacked first.  Nobody said it had to be perfectly flat....

That's my opinion on how to solve the problem and do what I think is the work required to produce a high quality result.  Without a lot more information, it's all just opinion on what the right procedure is to follow.  I believe you when you say the weld can be made in an hour.  But the prep work, dealing with the 3/4" gap will take a whole lot longer than just the welding.  Running the beads is the easy part of this job.  Hopefully all these varying opinions will help the original poster come up with the best solution to the problem.

I would encourage you to look at some other wire filler metals, if you're only experience is with 1/16" Coreshield 8.  That's a fine product, but it's not the fastest wire with the highest deposition rate available.  There are self-shielded products with deposition rates in the 10-20 lbs/hour range.  So no problems with needing gas in the field.  You'd need a big 400-500 amp machine with CV capability to run them, which I believe you have.(Yours is a Vantage 400 or 500, right?)  The original poster has a smaller engine drive, so some of the wires out there need more amperage than he can run.  Even large diameter E7024 needs more amperage than his welder can deliver.  Some of the flat position wires are 30 or more pounds per hour.  Not all of these big wires are suitable for this job, because the joints are only 1/2" plate.  But I believe you can find a wire that's faster than 7024.

Stick might still be the best option, if the original poster doesn't have much previous experience running wires.  I'll agree with you to the extent that it's faster to weld with the process you know best, rather than learn a new process in the field, 'under the gun'.

I'm not a contractor  nor an engineer! but why  wouldn't you cover all the base, and get a/an engineer or owner sign off on your  work to be done , then you could get a process that you were comfortable with and a known set of parameters to get the job done. with no liability to you! and bid the job accordingly.