You need an extended mirror clamped onto your stock mirrors , twisted at an angle so you can see your poptop Up . But this will be useless if you don't check your mirrors either
We've only got the original straps in each corner and we've never had a problem with them apart from this Easter when we were camping in Kent and storm Katy smashed up some awnings and threatened to lift our roof off of the van.
0 - 60 in 20 minutes as opposed to 0 - 60 in 40 minutes? Speaking from bitter experience the height barrier intervenes at 15 mph long before aerodynamics comes into play.
Said the ex driving instructor Good idea though, I usually forget to drop the roof after I've loaded the dog crate and have to unpack and reload
On a similar vein - I fit magnetic rain covers to the engine air vents and if I leave them on the engine gets HOT. So I tie a bit of ribbon to the steering wheel to remind me to take them off. I tried fluorescent aviation-style tags on the covers but I still didnt always notice them before driving off. Similarly you could hook a gonk onto the steering wheel to remind you of the poptop being up...
My forehead slapper is not switching off the headlights when I park. I thought of putting a clothes peg on some string and attaching the string to the door panel. Then when I pull the handle out (am NOT writing knob) I cd clip the clothes peg onto it. When I opened the door it'd pull it off or just be so obvious I'd remember. But any better ways?
I personally don't know how @Kkkaty but it can't be beyond the wit of mankind (or an auto electrician) to wire in a headlamp warning buzzer. I got mine from the bay of ease and it was only three or four pounds.
The first time you try to ride your motorbike away with the front disc lock on is usually the last (ask me how I know). Most of them now come with a bungee that attaches to the throttle much the same as @mikedjames ribbon on the steering wheel, good idea.
It was easy peasy Tom, it must've been 'cos I could do it. The body of the switch goes to earth, the spade connector on the switch goes to one wire of the buzzer and the other wire on the buzzer goes to a switched live. On my bus the three right most fuses are switched live.
Tie a cord to the wife and the poptop when she suddenly disappears you'll know it's up alternately if she s of well built size she'll hold anchor it down 
I think I need one of these Washing the bus today and discovered To front tip was sticking up a 1" I'm a very very lucky