Window sealing: PL adhesive instead of butyl tape

I am finally into installing my 15x18 Lil Bear awning windows. I measured the minimum needed clearance to insert the frame into the cut out, then made that cut with my Roto=Zip spiral saw (after installing guide plates). Then I used 60 grit on a palm sander to smooth. I then found that my measurements didn't account for the screws holding the frame together. I then made inlets at all four corners (I used my angle grinder-my favorite woodworking tool) to accommodate the screws. A very tight fit. Except at the bottom, which slants down towards the outside (I presume to promote drainage "weeping"). My question is: since I will need to seal the gaps at the bottom, and around the in-letted frame screws, can I just use PL adhesive to do so or must I also use butyl tape as well? I have a roll of BT25XL tape, but it will require more space to install and the PL will be waterproof anyhow.