The current water line is 1 1/2" sched 40 PVC. It runs a total of 2,145 feet from the meter to where the trailer used to sit. Elevation change +20 ft. I measured the pressure at the end of the line to be between 135 and 150 psi.

What accounts for the change in pressure measurement, time of day?

If any of those measurements were taken while water is flowing, that's not what you want for your design starting point. You want the static pressure, when there is no water flowing on your lateral. Of course if the utility piping upstream of your meter is not super large relative to the demand on it, you could be seeing 15 psi fluctuation in your static pressure just due to fluctuation in demand on your water main. So I'll assume for now those are all static measurements.

1-1/2" Schedule 40 PVC has an inner diameter of 1.61". So take as a baseline that your extension is also 1.61" ID, and let's see if that will work adequately. In other words, if you choose some type of PE pipe instead of 1-1/2" Sch 40 PVC, choose one with a larger ID than 1.61", rather than a smaller ID.

I understand your total run from the meter will be 2030 ft, with an elevation rise of 60 ft relative to where you measured static pressure. That 60 ft of rise is a loss of 26 psi. So your static pressure at the house would be 109 psi to 124 psi.

Per the calculator referenced earlier, with 10 gpm demand the 2030 ft Schedule 40 PVC 1-1/2" lateral (no allowance for fittings, so that should probably be bumped up a bit) would drop 6.0 psi. With 20 gpm it would drop 22 psi.

Pressure drop through the water meter itself is non-negligible, you could specify the water meter model to get more exact data, otherwise we can guess 3 psi drop at 10 gpm, 7 psi drop at 20 gpm.

With those numbers, and no PRV, your max static pressure at the house would be 124 psi; the min dynamic pressure at 10 gpm would be 100 psi; and the min dynamic pressure at 20 gpm would 80 psi.

So those numbers show no lack of pressure, but the house static pressure would be too high and you'll need a PRV. If your water lateral can handle the up to 160 psi you seem to have at the meter, then just using a PRV at the house would suffice. If you set the PRV at say 70 psi, then depending on the model, it might drop 4 psi at 10 gpm and 7 psi at 20 gpm. So just after the PRV you should see 63-70 psi depending on demand.

I'm not knowledgeable on the advisability of running your lateral at up to 160 psi; so it might be better to have a PRV at the meter. If you rely on just that PRV, and set it so your house static pressure is 80 psi (maximum advisable), then you'd see a much bigger swing in pressure at the house, from 80 psi static to perhaps as low as 50 psi with 20 gpm of flow.

I'm also not knowledgeable enough to say whether looking at 20 gpm performance is reasonable, or whether for a single family house it would suffice to look at 10 gpm or 15 gpm performance. Although if you have large irrigation demands, or fire sprinklers on the same water lateral, I can say that 20 gpm is in the ball park and you may need to consider even higher flow rates.

Hope this helps.

Cheers, Wayne