Yes, a motorhome will need an e-vignette.
Special rule for motorhomes: Motorhomes over 3.5 tonnes are NOT subject to the MYTO and also use the e-vignette.
Related articles:
What vehicles need a Slovak e-vignette?
Where can I buy the Slovak motorway e-vignette?
How much does the Slovak e-vignette cost?
What different types are available for the Slovak e-vignette?