Any trick to keeping the back straps tight? I'll pull them tight and within a day of driving they loosen up and it starts to sag/flap over the back seat. I know I could get top props but surely there is a way to keep the straps from loosening at the buckle.. hoping for some ideas

I have the sun bonnet BTW

 

I take the working end of the strap (the loose end) and tie a thumb knot around the strap as it enters the buckle. A thumb knot is basically an overhand knot tied around the strap itself. It helps some, but the wind forces pushing the top will probably make it necessary to adjust the straps on occasion.