If you want something to re-use year after year and not a shrink -wrap kit,
then use a Kal-wall type of product.
I’ll get you a pic & a specification. Below is it. Kal-wall will last 20 years, but will cost probably 1.5x more.
Ok, here’s the solution: https://www.ameriluxinternational.com/Newsletters/Newsletters_2019/AmeriLuxNewsSeptember2019.pdf
This is the factory’s DIY Newsletter for what you want to do.
Menards stocks the 6mm Twinwall, it looks similar to the green checkmarked product in the Newsletter.
I also wish we could use something to do that. a 4' X 8' panel of plexiglass is about $100 and would need to be framed. Then there is (off season) storage. How high are the screen panels on your porch? My brother in law bought sliders with screens/glass to close in a porch they have and got a great price but his situation was easily adapted to the available product.
Build wood frames out if 1X2 firing strips to fit the windows. Staple thick clear vinyl to the frames. Screw the frames to the window frames.
Here is another style of vinyl panels:
If your actually going to use the room in winter, I would suggest some polycarbonate panels which are more rigid than vinyl.... the ones with channels would even provide some insulation value..... https://www.google.com/search?client=opera&q=smooth+polycarbonate+panels&sourceid=opera&ie=UTF-8&oe=UTF-8 they are very lightweight and some versions you can cut with tin snips/scissors