Redcollie Watercolour Stretchers have been selling internationally online for over 16 years and are proven to be a simple solution to the problem of keeping watercolour paper flat while painting. They do away with the need for gumstrip tape for ever. 

I developed these when teaching watercolour painting, realising that many people had problems stretching paper by conventional gumstrip: get the paper too wet and it doesn't stick to the board, and even if it does it can sometimes tear free as it dries. 

Ideally suited for papers up to 300gsm these stretchers are lightweight and easy to use, enabling the watercolourist to stretch a sheet of paper in as little as ten minutes. 
The binders are slightly thicker than the board, meaning a ruler can be used to steady the hand over the painted surface and the stretchers can be placed face-to-face to protect the paper in transit. 

When the painting is complete the binders are removed and the painting is ready for mounting and framing. (I favour block-mounting and waxing, which does away with the need for framing and glass, giving a more modern appearance.)

They come in various popular sizes: A3, A4, Quarter Imperial. 

The A4 board is 30 X 21 cm (12x8 inches)

They come complete with the binders to hold the paper on the board and full instructions as to their use.

The paper is soaked as normal, then fixed to the board with the two-part binders. A hairdrier can be used to dry the paper if required, or if working wet-on-wet you can start painting immediately.