Hi, I'm surprised that nobody has responded to your question. I don't have a Kubota but I can't imagine the design varies too much from the OTC on my JD2520. I got it last year (south central Wisconsin too) just before a sub-zero cold snap. Wow... should have done that years ago! My 2520 is comparable to your
L2501; again, I'm guessing the cabs would be too. The rear cab section, behind the seat, is covered by the equivalent of 'leaving your shirttail out'. The vinyl just hangs below to just above the upper control arm.
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Does it 'block' the opening? Pretty well actually. You won't feel a draft or wind. I'm not compelled to improve mine (I wouldn't know how to actually... a lot going on in that section of the tractor). Regarding the heater, I don't want one. In fact, when I bought, OTC had a promotion and
gave me a 12V heater with the order. I didn't install and gave it to a friend for his cab'd Mule. Ease of installation/removal is important to me (kiss). I was comfortable with a coat on in that 10 day sub-zero snap. When the weather is in the 20's... the full winter coat is a bit much. Remember, you're putting an enclosure up against a machine that is rejecting heat as it chooches.
My cab is in the basement right now because I am about the fab a wooden lift beam tool before re-installing it this year. TTWT has a few videos showing his installation method... pretty wonky. I have an open post in the "Snow Blowing" section here asking for installation ideas; 2 responses so far. One lifts it off then stores up to his garage rafters and the other takes it all apart. I really want to leave it together (again, ease of install is important to me.) I just finished installing a box rail to the ceiling of my shop. I bought a single 'truck' in it to carry a simple deer hoist pully system. The plan is to park the tractor centered under the rail, snap the lift beam to the cab, attach to the hoist, lift cab , slide over the tractor from the rear, and lower down. I'll post results and pics by week's end probably. Hope this helps!