Lotta good joojoo on this thread!
Great technical posts Wayward! Really good info!
As to weight, the new PD4500 series are quite a bit lighter than the old unit you replace. You will probably come out close to even with the over all modern 50amp system vs. the ancient 30amp one, weight wise.
You will need to run a heavy wire from the PD4500 to where you connect your shore power. Guys can argue this, and there is some "slop" in how you interpret the electrical code. A friend of mine, who is a very good electrician, said I could use an 8 gauge wire for this. Reading the code one way, you could. But if you looked at a little differently, the 8-wire was marginal. So, I used a 6-wire (you get into amp capacity at temperatures, etc.).
My biggest issue was the old one was short and wide, the new one was tall and narrow. I didn't want to mount the new panel sideways, so I had to modify the cabinet. I had to "fill in" on the sides and open up top and bottom a bit (fortunately I had room to do this and keep the panel in the same location), then I had to make a spacer to set the new panel 3/4 inch in toward the center of the coach because the PD4500 was a little deeper than the univolt. But, it made a nice install. I routed the 6 wire through the cabinets, under the floor, across the belly pan between frame rails, and popped back into the compartment where the shore power plug was supposed to go. Make sure to use appropriate supports and "pads" to keep the wire from ever getting chafed.
Originally, I had 40' of 30amp chord that the PO had hardwired to the coach, so I had to coil that up every time and stuff it into the compartment. But with the 50amp, I have two stand alone chords. One is a 30 footer, the other is a 15 footer. Depending upon how the campground is configured, I'll use one, the other, or both. I have a 30 to 50amp adapter pigtail for the places that only have 30amp (like my garage plug that I wired up many moons ago) and 20amp to 30amp plug to use the genny.
Thus far it's worked well for me.
The 50amp chords aren't that bad to wind up. I have two big Rubbermaid boxes I store them in. Keep one under each side of the dinette. If they lay in the sun, they flex pretty well. If it's cold out, they can be a bit stiff. But nothing to worry about. They make high flex 50amp chords, but they cost double what the normal ones do, and the normal ones aren't cheap.
I only have one a/c unit, but it's a 15,000btu and it does a very good job. Here's another trick for you: Paint the roof high gloss white. I did that first, and that alone cut the temp gain by 10 deg. F alone. That allowed my tired old 13,500 a/c to cool her down. But when it finally died (and I'd run it on a hot wired control board for a year....two toggle switches, for fan on/off and compressor on/off and no thermostat control....it was safe, but you'd wake up in the middle of the night and see your breath....) I decided to get a 15,000btu. If you do both of these mods, I'd bet one a/c would do you just fine.
Hope this helps!