This self adhesive framing tape is available in 50 metre rolls in 3 widths. It is perfect for attaching your watercolour paper securely to your drawing board and I would recommend this above traditional gummed tape for the job any day - it is just so much quicker and less fiddly with this.
It also provides quick and accurate sealing of the backboard into the back of your frame when you come to framing your finished painting ready for sale.
(p.s. Please note that if you are going to use this tape when stretching watercolour paper you must ensure you leave a dry edge round your sheet for it to adhere to.)