I didn't know Winegard made a 30dB amp. I know Channel Master does (CM7777), but it doesn't have individual inputs for UHF and VHF. The leads into a UVSJ or dual-input amp don't have to be the same length.
The 'preamp' I was referring to is what you have on the mast, under the antenna, existing only to push the signal down a long run of coax and through splitters.
30dB is pretty stiff for a preamp. Hopefully it doesn't overload on the stronger signals. That sort of thing is why folks usually recommend testing with no amplifier and a short RG6 coax straight to one tv (even through a window, or put the tv outside on an extension cord) to get a real baseline, and go from there. If that's not feasible, then there's really nothing wrong with combining the two antennas into the amp, aimed as best you can using a real compass (cel phone compasses can give a different answer each time you use it, sometimes off by a lot), and trying it. If it works to your satisfaction, then great. It's a bit of a crap shoot, though, especially with weaker 1-edge and 2-edge signals.
There are lots of sources for UVSJ units, like Solid Signal, Radio Shack, Antennas Direct (a nice outdoor unit to mount to the mast
https://www.antennasdirect.com/store...Combiners.html), and others. Make sure it's actually a VHF-UHF combiner, not just a 2-way splitter. The mast mounted types are actually made for the weather, and the indoor types would have to be sealed up against weather, so in your case, I'd probably do the outdoor type and still seal up the F-connectors.
And for a little more money, an amp with separate VHF and UHF inputs (with a built-in FM filter) would be simpler, with fewer connections out in the weather.