These specs say you are prewired for solar. Typically, these specs are lifted directly from the manufacturer. (Search - Ctrl+F - "solar" no quotes).
Let's assume you are prewired for solar. Do you have, or do you remember a sticker inside that tells you where the wire is routed and where to locate a solar charge controller? If so, problem solved. There is a
connector gland on the roof with #10 AWG wire coming down to the solar charge controller location (sticker) and on from there to a parallel connection to the wires between the battery bank and the converter.
#10 AWG can handle about 30 amps DC...depending on distance. (wire distance with DC is out and back...a 10' wire pair is 20 feet long in the DC world.) That equates to 400 watts of solar on the roof if wired in parallel (ideal). More if wired in some mix of series and parallel. As with other commenters, I'd upgrade to at least 400 watts of solar. If you want to do more, come back for info about how to do a mix of series and parallel, and the advantages and disadvantages of each. (Solar panel voltages and currents are a big topic, so that can wait until you see if you are pre-wired for solar.)
So, step 1 is look for the sticker. Step 2 is climb on the roof and look for the gland. If you have a gland and no sticker, contact the manufacturer and ask where the sticker should be...precise measurements. My hunch, given your floorplan, is that it's on your pantry wall...and the slide might hide it when the slide is closed. It could also come down through the cabinet surrounding the fridge. MOST likely, the gland will be directly above where the wire to the sticker is routed. It might be in the bunk area on the fridge wall separating the fridge and bunks. It won't be over the stove.
All that said, the specs might be wrong. Since you have a travel trailer (not a 5th wheel) using a vent pipe as conduit might not work. And sewer gasses are corosive anyway.
If you must Rube Goldgerg it, I'd probably locate the gland ABOVE the pantry, run the wire down through the roof, into the pantry, through the back or side of the pantry and straight out the bottom of the floor...outside the frame. I'd locate the charge controller on the slide side wall of the pantry...recess mounted to allow the slide to operate without interference (check for clearance first). I'm guessing your furnace is under your fridge, but if the furnace is below the pantry, there's no reason you can't run the wired down through there. You MIGHT have to remove the furnace, but probably not. Even if you must remove the furnace, it's just some flex duct, a couple of screws and the propane line. You can probably leave the wiring attached.
I'd use
#8 AWG wire for the whole run STRAIGHT TO THE BATTERY bank wired in parallel right at the battery terminals. Install an
inline fuse near the battery rated at about 40 amps. Using the pantry to route your wire will be much neater than the path you are considering.
I installed a small inverter way back near the rear of my rig...wired straight to the battery...using the same wire. This is overkill, but I drilled the frame outriggers, lined the holes with rubber gromets, used conduit over the axles, and straight up through the coroplast, into a space that holds a heat duct, and up to the inverter. More or less the reverse of what you'd do. You could also zip-tie the wire to the coroplast pretty easily. My rig is a 2020, and the wire jacket is like new even though it is "outside" under the trailer.
If you want to pursue any of this, just hit me up.
BTW, the 8 gauge wire will handle that distance. I'd buy the 50 foot roll, because you'll end up using the rest for another project...say a 500 watt inverter to run a Starlink.
PS The best tool for recess mounting the solar charge controller is an
oscillating tool. Get a premium (e.g. Diablo brand) blade to make a perfect cut. A cheap tool with a $15 blade is a great investment. If you have a cordless drill, buy a bare tool that can share your batteries.
