Draining water out of boot lid?

After a period of very heavy rain, there's loads of water inside the boot lid on my 1990 cabriolet.
How on earth do I get it out? I've tried opening and shutting the lid vigorously, and can hear lots of sloshing about.
Feels like I need to turn the car upside down and shake it! I can't see any obvious drainage hole or anything. 

Boot lock seal is probably the reason why it's filling up with water, you should be able to remove the cardboard trim and have a look inside the boot lid to see if you have water on there.

Something like this, loads about so shop around.
https://www.classic-vw.co.uk/mk1-golf-cabrio-boot-lock-seal-161827527-4676-p.asp

You can either suck it out with a shop vac via the Cardboard cover being removed.

You can drill a 1/8 hole in the bottom on each corner about 2 inches in and cover with a piece of Duct tape or find a rubber plug that is flat,  You need to inspect and repair where it is leaking in from As you will see a Water track usually from the lock.

https://www.amazon.com/Premium-Store-Small-Rubber-Plugs/dp/B074WL8KVH

I have a How-to on that in the archive section, about where is my car leaking.

Thanks both! I'll get on it, as soon as it stops raining!

Edit to add: Wow, Briano1234 - just found all your how-tos! I'll be using a few of those.