If the vinyl window frame can hold the blind, you can process it as inside mounting.vinyl windows is that they are not strong enough to withstand the weight of blinds. It is because of this reason that it is not advisable to screw the brackets directly onto the vinyl channel which holds the window together. For this reason, the brackets need to be fixed at the top or on the sides of the inside opening or outside. Never drill through the actual frame of the window but only drill through jamb extensions. If you plan to install them inside the opening you must ensure that the blinds’ bottom does not bang into the vinyl finger-hold located at the bottom.